The present invention relates to an aircraft having a variable geometry for adapting the flight characteristics and, further, to the use of such an aircraft or a method for changing the geometry of the aircraft during the flight.
Airplanes with variable geometry are sometimes referred to as “swing-wing aircrafts” (e.g. “Grunmann F-14 Tomcat”, “Mikojan-Gurewitsch MiG-23 and MiG-27” etc.). These known aircrafts comprise a fuselage with a pair of wings projecting therefrom in the transverse direction. Each of the wings has an inner wing section arranged stationarily with respect to the fuselage and an outer wing section adjacent thereto and pivotable about a pivot axis. The pivot axis is substantially oriented in the vertical direction of the aircraft.
By means of the pivotability of the outer wing sections of such a swing-wing aircraft, the sweep of the wings, and thus the geometry (“configuration”), can be varied during the flight so as to advantageously adapt the flight characteristics (e.g., air resistance, uplift, maneuverability etc.), to take account of the respective requirements in different flight situations (e.g. take-off and landing, cruise flight, military combat missions etc.). It is known that a rather small sweep is advantageous, for example, for an energy-efficient flight over large distances (cruise flight), whereas a larger sweep is particularly advantageous for reducing the air resistance during a particularly fast flight.
However, the known aircrafts with variable geometry also have disadvantages. Besides the need to install a pivoting drive for pivoting the wings, which increases the weight, there is, for example in the military sector, an increasing demand with respect to a “low radar signature shape” in order to avoid radar detection or ranging of the aircraft or at least to make it difficult. Additionally, this field of application typically requires an energy-efficient cruise flight, as well as maneuverable and agile flight characteristics, as in case of a combat aircraft, within one flight mission. The design objectives for an aircraft which meets these requirements are complementary. A particularly energy-efficient cruise flight is only possible with wings having a high aspect ratio (slim wings). However, such wings reduce the agility due to the relative high moment of inertia about the longitudinal axis of the aircraft. Moreover, slim wings make it difficult to design suitable pivoting kinematics for a predefined wing area.
Exemplary embodiments of the present invention provide an alternative approach for an aircraft with variable geometry by providing a simplified “pivoting drive”, which makes the aforementioned conflict of objectives more manageable in order to broaden in this manner the field of use of the aircraft.
In accordance with exemplary embodiments of the present invention, the pivot axis of the wings of an aircraft is oriented in a direction which deviates by a maximum of 40°, preferably by a maximum of 20°, from the longitudinal direction (corresponding to the flight direction) of the aircraft.
For example, the pivot axis can be oriented substantially in the longitudinal direction. This refers, in particular, to orientations deviating by a maximum of 20°, preferably by a maximum of 10° from the longitudinal direction of the aircraft.
If the pivot axis is not exactly oriented in the longitudinal direction, then in accordance with exemplary embodiments of the present invention, an inclination angle of the pivot axis with respect to the horizontal plane is smaller than an inclination angle of the vertical plane which is spanned by the longitudinal direction and the vertical direction.
Due to the pivotability of the wing sections about the pivot axes, which are oriented to a greater or lesser extent in the longitudinal direction, it is advantageously possible to fulfill flight missions with one and the same aircraft for which missions otherwise at least two different airplane configurations would be required. This would require the energy-efficient configuration with non-pivoted outer wing sections and thus “stretched” wings and at least one more agile configuration with pivoted outer wing sections and thus “effectively shortened” wings.
Further particular advantages of the invention are that the aircraft can be configured with a low radar signature (in particular also in the pivoted state of the wings) and that the pivoting mechanism does not need a separate pivoting drive specifically provided for pivoting. In fact, pivoting can be carried out by utilizing aerodynamic forces which act on the outer wing sections during the flight.
The terms “inner” (wing sections) and “outer” (wing sections) relate to the arrangement in the non-pivoted state in which, viewed in the transverse direction, the outer wing sections are farther out than the inner wing sections. To simplify matters, these designations for the two different wing sections are also used for the pivoted state although these designations are not quite correct because in a pivoted state, viewed in the transverse direction, the “outer wing section” can be arranged in approximately the same position as the “inner wing section”.
The term “fuselage” in the meaning of the invention is to be understood in a broader sense as the central region of the aircraft viewed in the transverse direction. In one embodiment, the aircraft comprises a “conventional fuselage” in the meaning that the latter can be clearly distinguished or differentiated from the wings projecting therefrom on both sides (a typical example for this is an approximately “cigar-shaped” elongated fuselage). In another embodiment, which is known among experts as “flying wing configuration”, the aircraft comprises no defined fuselage or fuselage that can be clearly differentiated from wings projecting on both sides. In this case there is a fluent transition between fuselage and wings or, in the extreme case, the fuselage is formed, when viewed in the transverse direction, by the inner ends of the inner wing sections themselves. In case of the latter “flying wing type”, the central portion of the aircraft, when viewed in the transverse direction, can be considered as the fuselage.
The present invention is particularly suitable for military applications, be it as an unmanned aircraft or as a manned aircraft.
In one preferred embodiment, the aircraft comprises a control device for actuating automatic pivoting of the outer wing sections during the flight due to an actuation command and/or in dependence on at least one airplane status parameter.
Such a control system can be part of a so-called avionics (flight control system) or can be connected thereto for implementing automatic pivoting in order to adjust, for example, control elements provided on the outer wing sections such as rudders (“ailerons”) or other adjustable, aerodynamically effective wing parts (e.g. flaps on the upper or lower wing side).
In case of a manned aircraft, adequate actuation commands for initiating automatic pivoting can be provided by corresponding operating commands of a pilot. In case of an unmanned aircraft, actuation commands can be transferred to the aircraft via a remote control system, which is available anyway for controlling the aircraft. In both cases, actuation commands can also be generated alternatively or additionally in an automatic manner (e.g. by an “autopilot” or another automatically operating flight control), for example to adapt, in case of a predetermined flight route, the properties of the aircraft to the local requirements (for each of the actual route sections).
Flight condition parameters which, for example, can be used as sensorially detected measurands alternatively or additionally to actuation commands for initiating and/or carrying out a pivoting process, can comprise, for example, the current airspeed (preferably the “true airspeed”), the current aerodynamic load situation, accelerations in different directions, angular acceleration about different axes etc.
According to one embodiment, the aircraft comprises a stabilizing mechanism in the region of the pivot axes for locking the outer wing section in the non-pivoted state against undesired pivoting, for example, by aerodynamic forces or also by inertial forces. In case of outer wing sections that can be pivoted upwardly, ascending forces have to be considered which, without such a locking mechanism, could cause undesired upward pivoting of the outer wing sections.
According to one aspect of the present invention, the stabilizing mechanism can be actuated using a control device in such a manner that by inactivating or at least reducing the locking effect, pivoting can be initiated by aerodynamic forces acting on the outer wing section. Alternatively or additionally to utilizing aerodynamic forces as “pivoting drive”, it is also possible to provide an additional drive, for example, an electric drive that can be located in the region of a mounting device defining the respective pivot axis.
For example, if it is intended, starting from the non-pivoted state of the wing, to pivot the outer wing sections upwardly, the uplift already present at the outer wings sections can advantageously be utilized for initiating this pivot movement. For this it is only necessary to suitably reduce or completely eliminate the locking effect. In particular, in the latter case it is advantageous if the outer wing sections are provided with adjustable control elements (in the simplest case, e.g., ailerons), which can be suitably actuated for a pivoting process which is partially or completely carried out by aerodynamic forces. This can be carried out, for example, by the mentioned control device, if necessary in connection with an avionics system.
The pivot movement is preferably provided with a pivoting angle of at least 110°, preferably at least 120°. When starting from a non-pivoted state of the outer wing sections, more than one additional pivoting state can be taken, thus at least one “intermediate position” can be actuated in steps or continuously variable, the aforementioned pivoting angles are to be understood as the angle difference between non-pivoted state (“stretched wings”) and “maximally pivoted state” (end position).
The term “stretched wing” designates, for example, an arrangement of the outer wing sections with respect to the inner wing sections, wherein the planes spanned by these two wing sections are substantially congruent or intersect at most at a small angle.
According to an advantageous embodiment, the edges of the free ends of the outer wing sections extend parallel to each other in the maximally pivoted state, in particular both substantially in the longitudinal direction of the aircraft (so that they can contact each other without gap).
In one embodiment, the aircraft comprises a stabilizing mechanism (if applicable, further stabilizing mechanisms) for locking the free ends of the outer wings in a pivoted state, in particular the “maximally pivoted” state. There are different possibilities for such a locking mechanism:
In one embodiment, the aircraft comprises, for example, a stabilizing mechanism arranged on the fuselage for locking the free ends of the outer wings sections to the fuselage and/or to each other.
According to another embodiment, such a stabilizing mechanism is arranged at a vertical tail (in particular at the free end of the same) projecting from the fuselage in the vertical direction.
According to another embodiment, such a stabilizing mechanism is arranged at a horizontal tail projecting from the fuselage on both sides in the transverse direction.
Yet another embodiment of such a stabilizing mechanism provides, for example, that the latter is arranged at the free ends of the outer wing sections themselves so as to fix the free ends of the pivoted wing sections to each other (if applicable, without connection to the fuselage or spaced apart from the fuselage of the aircraft). For implementing this embodiment, coupling elements which can be brought into engagement with each other can be provided at the free ends of the outer wing sections.
As already mentioned, according to one embodiment, the aircraft does not have a defined fuselage. In this embodiment, the payload can be accommodated in the wing sections. The aircraft propulsion can be integrated at the wings, for example, in the region of the pivot axes. At an inner rigid wing (“inner wing sections”), at the lateral ends of the same, the pivotable “outer wing sections” are mounted, wherein their lateral outer ends can preferably be connected and locked to each in the pivoted state.
In a preferred embodiment the pivot axes are arranged in such a manner that the wingspan of the aircraft can be substantially halved by pivoting. In this respect the wingspan can be reduced by a pivoting process by at least 40%, in particular at least 50%.
In one embodiment the wing has a positive leading-edge sweep and/or a positive trailing-edge sweep in the non-pivoted state.
If, in the non-pivoted state, the outer wing sections as such have a positive sweep at the leading edge and/or the trailing edge, it is possible through a suitable selection of the orientation of the pivot axes to achieve a negative sweep at the leading edge or the trailing edge in the pivoted state (if the outer wing sections were pivoted far enough), which is advantageous for many applications or flight situations.
It should be noted in this connection that the sweep angles of the outer wings in the non-pivoted state and in the pivoted state can be selected largely independent of each other. Based on a certain sweep in the non-pivoted state, the sweep in the pivoted state is primarily determined by the orientation of the pivot axes which can be selected accordingly.
In one embodiment a course of the leading edge of the outer wing sections is offset backward with respect to a course of the leading edge of the inner wing sections and/or a course of the trailing edge of the outer wing sections is offset backward with respect to a course of the trailing edge of the inner wing sections. Such an offset of the wings often offers aerodynamic advantages, in particular in the non-pivoted state, by reducing the air resistance.
In one embodiment, the outer wing section has a substantially symmetrical wing profile. It has to be considered here that in case of a sufficiently large pivoting movement of the outer wing section, the upper side and the lower side of the latter are “interchanged”. In this respect, an asymmetric profile which, for example, provides an uplift in the non-pivoted state, would often be disadvantageous due to a descending force in the pivoted state. From this point of view, as already mentioned, providing the outer wing sections with controllably adjustable, aerodynamically effective control elements (e.g. rudders etc.) is very advantageous so as to be able to set the aerodynamic effect of the outer wing section depending on the actual pivoting state by a suitable adjustment of such elements. Preferably, the wing sections are each provided with one rudder (“aileron”) extending substantially over the entire length (wingspan) of the respective wing section (e.g. over at least 90% of said length) so that it can assume the function of a so-called plain flap.
According to a first aspect of a method for changing the geometry of an aircraft according to the invention, this change takes place during the flight by utilizing aerodynamic forces which act on the outer wing sections.
These forces depend, for example, on the current flight condition so that by suitably controlling the aircraft, such an “aerodynamic pivoting drive” is possible for both pivoting directions. In one aspect of the present invention, the outer wing sections themselves are provided with adjustable, aerodynamically effective control elements, preferably rudders, at the trailing edges of the wing, so that more or less depending on the current flight condition, a suitable pivoting movement of these control elements can be carried out.
Control flaps and/or rudders arranged on the outer wing sections can be configured in such a manner that by adjusting the same, a pivoting movement of the outer wing sections in the two pivoting directions can be effected. For rudders at the trailing edges of the outer wing sections this can mean that they can be pivoted upwardly as well as downwardly out of a central plane of the outer wing sections.
According to one development of this method for changing the geometry of the aircraft, the aircraft is equipped with a stabilizing mechanism arranged in the region of the pivot axes and this stabilizing mechanism counteracts the pivoting movement with a certain resistance. Such a “pivoting brake” can advantageously prevent pivoting being carried out too fast. Moreover, by such a “damped pivoting”, the control effort for actuating control elements on the outer wing section during pivoting can be advantageously simplified. According to one aspect, when carrying out the pivoting movement, an auxiliary pivoting mechanism is used by means of which, if necessary, a torque decelerating the pivoting movement and/or a torque supporting the rotational movement can be exerted on the respective outer wing section. The need for a decelerating torque or a supporting torque can arise already in the design phase for predetermined portions of the pivoting process. Alternatively or additionally, such a need can also be determined by a control unit through a control algorithm based on a sensorial detection of parameters of the pivoting movement (e.g., current pivoting angle, current angular velocity of the pivoting movement etc.), whereupon said control unit actuates the auxiliary pivoting mechanism accordingly.
According to a further development of the above-illustrated method for changing the aircraft geometry, the pivoting movement is controlled in such a manner that, based on a sensorially detected pivoting angle position and a desired pivoting movement (e.g., chronological pivoting course), an adjustment of aerodynamically effective control elements of the aircraft, for example, of control flaps or rudders on the outer wing sections, takes place. According to one aspect, such a controlled or regulated adjustment of control elements during pivoting can also be combined with the actuation of the aforementioned auxiliary pivoting mechanism.
According to a second aspect of the method for changing the geometry of the aircraft, which can also be combined with the first aspect, it is provided that the change of the geometry (by pivoting the outer wing sections) during the flight takes place in a flight condition with significantly reduced aerodynamic forces, in particular, for example, at the outer wing sections. This reduces the risk that by initiating the pivoting movement, although the resulting changes of the aerodynamic conditions with respect to flight stability are too drastic. In case of an aerodynamic pivoting drive, this measure prevents the pivoting movement from being performed too fast. In case that, alternatively or additionally, a separate drive (e.g., electromotive drive) or the mentioned auxiliary pivoting mechanism is employed for initiating the pivoting movement, this results advantageously in low requirements with respect to the performance of such a drive or such a mechanism.
The term “significantly reduced aerodynamic forces” covers in particular such forces that effect a torque acting on the outer wing section with respect to the pivot axes and which is not more than 50%, preferably not more than 25% of the torque which results from a normal straight and level flight (cruise flight).
In this respect, for example, carrying out the pivoting movement can be provided during a so-called parabolic flight. The aerodynamic forces acting during a parabolic flight are largely reduced so that this specific flight condition can be advantageously used within the context of the invention for changing the configuration of the aircraft.